Dirt pick-up resistant composition

ABSTRACT

Water-based compositions that are resistant to dirt pickup, efflorescence, tannin bleed-through and surfactant leaching are described. The water-based composition includes a latex or water-dispersible polymer and a non-VOC UV-VIS (preferably, ultraviolet) absorber as a dirt pickup resistance additive. Methods of making water-based compositions including a non-VOC UV-VIS absorber as an additive are also described.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of U.S. patent applicationSer. No. 16/241,461, filed 7 Jan. 2019, which is a continuation of U.S.patent application Ser. No. 15/665,566, filed 1 Aug. 2017, which is acontinuation-in-part of U.S. patent application Ser. No. 15/295,264,filed 17 Oct. 2016, which is a continuation-in-part of U.S. patentapplication Ser. No. 14/770,123, filed 25 Aug. 2015, which is a § 371national stage entry of PCT Application No. PCT/US2014/020719, filed 5Mar. 2014, which claims priority to U.S. Provisional Application No.61/836,884, filed 19 Jun. 2013, and U.S. Provisional Application No.61/799,995, filed 15 Mar. 2013, each of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

A water-based composition with low volatile organic (VOC) content suchas a paint, seal, coat, caulk, etc. is exposed to contamination from theatmosphere from the moment it is applied. This contamination includesdirt and dust which are carried to the surface by rain, airbornemoisture droplets, wind currents, or direct physical contact withpeople, animals, or other objects. Dirt can be either organic orinorganic. Examples of dirt particles include sand, smoke particles,dust, metallic fibers, carbon black, rust, grease, pollen, humandetritus, and fungal spores. Dirt particles attract moisture to thesurface of the composition. This moisture provides a suitableenvironment in which microbial spores may survive and proliferate intocolonies, thus further contributing to the unsightly appearance of thesurface. Accordingly, water-based compositions can acquire a dirty andunsightly appearance because of the amount of dirt that clings to them.Similarly, paints used on exterior masonry walls or wood siding oftenexperience staining and paint loss as a result of efflorescence, tanninbleed-through, surfactant leaching, and other effects.

Previously, the paint industry has used compounds like benzophenone toaid in the dirt pickup resistance of water-based paints, specificallywater-based acrylic coatings. However, there is a general desire in theindustry to reduce VOC emissions to at or near-zero levels, therebyreducing the environmental and health impact of paints. Benzophenone isconsidered a VOC and its use as a dirt pickup resistance additive inwater-based paints increases the VOC emissions of the paint.

Accordingly, there is a need for effective low VOC compositions thatresist dirt pick up and resist efflorescence, surfactant leaching,tannin bleed-through and other similar effects when used as exteriordurable paints, and do not compromise the required application andperformance properties desirable for finished surfaces in the paintindustry.

SUMMARY

The present disclosure provides water-based compositions, such ascoating compositions that can resist dirt pick-up and reduce oreliminate surfactant leaching, efflorescence, tannin bleed-through andthe like. The compositions contain a latex or water-dispersible polymerand a non-VOC UV absorber, along with methods for making suchcompositions.

In an aspect, a water-based coating composition is provided, including alatex or water-dispersible polymer having a Tg of about 5 to 20° C. anda non-VOC UV absorber capable of absorbing UV radiation within a rangeof 240 to 400 nm. The composition may optionally include a crosslinkingcomponent. The UV absorber is present in an amount sufficient to preventsurfactant leaching, efflorescence, or tannin bleed-through when thecoating composition is applied to an exterior substrate surface, asassessed by ΔE values obtained on accelerated testing.

In another aspect, the present disclosure provides methods of making adirt pickup-resistant composition, including steps of providing one ormore ethylenically unsaturated monomers in an emulsion, polymerizing theemulsion, and adding a non-VOC UV absorber to the polymerized emulsionin an amount sufficient to produce a coating composition with improveddirt pickup resistance relative to a conventional coating based on ΔEvalues.

In yet another aspect, the present disclosure provides a water-basedcomposition consisting essentially of a latex or water-dispersiblepolymer in water derived by polymerization of an emulsion of one or moreethylenically unsaturated monomers, and a non-VOC UV absorber capable ofabsorbing UV radiation within a range of 240 to 400 nm. The non-VOC UVabsorber is present in an amount sufficient to produce a coatingcomposition with improved dirt pickup resistance relative to aconventional coating composition based on ΔE values.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through lists of examples, which can be used invarious combinations. In each instance, the recited list serves only asa representative group and should not be interpreted as an exclusivelist.

The details of one or more embodiments of the invention are set for inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

Selected Definitions

Unless otherwise specified, the following terms as used herein have themeanings as provided below.

The term “water-dispersible” in the context of the polymer means onethat is itself capable of being dispersed in water for creating adispersion or emulsion of polymer particles in water having at least onemonth shelf stability at normal storage temperatures.

The term “dispersible” in the context of a dispersible coalescent meansthat the coalescent can be mixed into the water-based composition oflatex or water-dispersible polymer particles to form a uniform mixturewithout the use of high shear mixing.

The term “stable” in the context of a water-based composition containinga dispersible coalescent means that the coalescent does not phaseseparate from the water-based composition upon standing at 120° F. (49°C.) for at least four weeks.

As used herein, the terms “volatile organic content” and “VOC” refer tothe volatility of the composition as measured by ASTM D6886-14e1(Standard Test Method for Determination of the Weight Percent IndividualVolatile Organic Compounds in Waterborne Air-Dry Coatings by GasChromatography). This test uses methyl palmitate as a reference marker.A compound that elutes prior to the marker is considered VOC while acompound that elutes after the marker is not considered VOC. As usedherein, the term “non-VOC” refers to compounds that elute after themethyl palmitate marker, or “exempt” from VOC in that the compounds thatelute prior to methyl palmitate but are known to be less volatile thanmethyl palmitate, such as acetone and t-butyl acetate, for example. Theterm “exempt” may be used interchangeably with “non-VOC” when referringto a component of the compositions described herein.

The term “essentially free of VOC” means that the compositions describedherein contain less than 5 g/L of VOCs. The terms, “zero VOC” and“essentially free of VOC” are used interchangeably herein.

As used herein, the term “organic group” means a hydrocarbon group (withoptional elements other than carbon and hydrogen, such as oxygen,nitrogen, sulfur, and silicon) that is classified as an aliphatic group,cyclic group, or combination of aliphatic and cyclic groups (e.g.,alkaryl and aralkyl groups). The term “aliphatic group” means asaturated or unsaturated linear or branched hydrocarbon group. This termis used to encompass alkyl, alkenyl, and alkynyl groups, for example.The term “alkyl group” means a saturated linear or branched hydrocarbongroup including, for example, methyl, ethyl, isopropyl, t-butyl, heptyl,dodecyl, octadecyl, amyl, 2-ethylhexyl, and the like. The term “alkenylgroup” means an unsaturated, linear or branched hydrocarbon group withone or more carbon-carbon double bonds, such as a vinyl group. The term“alkynyl group” means an unsaturated, linear or branched hydrocarbongroup with one or more carbon-carbon triple bonds. The term “cyclicgroup” means a closed ring hydrocarbon group that is classified as analicyclic group or an aromatic group, both of which can includeheteroatoms. The term “alicyclic group” means a cyclic hydrocarbon grouphaving properties resembling those of aliphatic groups. The term “Ar”refers to a divalent aryl group (i.e., an arylene group) which refers toa closed aromatic ring or ring system such as phenylene, naphthylene,biphenylene, fluorenylene, and indenyl, as well as heteroarylene groups(i.e., a closed ring hydrocarbon in which one or more of the atoms inthe ring is an element other than carbon (e.g., nitrogen, oxygen,sulfur, etc.)). Suitable heteroaryl groups include furyl, thienyl,pyridyl, quinolinyl, isoquinolinyl, indolyl, isoindolyl, triazolyl,pyrrolyl, tetrazolyl, imidazolyl, pyrazolyl, oxazolyl, thiazolyl,benzofuranyl, benzothiophenyl, carbazolyl, benzoxazolyl, pyrimidinyl,benzimidazolyl, quinoxalinyl, benzothiazolyl, naphthyridinyl,isoxazolyl, isothiazolyl, purinyl, quinazolinyl, pyrazinyl,1-oxidopyridyl, pyridazinyl, triazinyl, tetrazinyl, oxadiazolyl,thiadiazolyl, and so on. When such groups are divalent, they aretypically referred to as “heteroarylene” groups (e.g., furylene,pyridylene, etc.)

A group that may be the same or different is referred to as being“independently” something. Substitution is anticipated on the organicgroups of the compounds of the present invention. As a means ofsimplifying the discussion and recitation of certain terminology usedthroughout this application, the terms “group” and “moiety” are used todifferentiate between chemical species that allow for substitution orthat may be substituted and those that do not allow or may not be sosubstituted. Thus, when the term “group” is used to describe a chemicalsubstituent, the described chemical material includes the unsubstitutedgroup and that group with O, N, Si, or S atoms, for example, in thechain (as in an alkoxy group) as well as carbonyl groups or otherconventional substitution. Where the term “moiety” is used to describe achemical compound or substituent, only an unsubstituted chemicalmaterial is intended to be included. For example, the phrase “alkylgroup” is intended to include not only pure open chain saturatedhydrocarbon alkyl substituents, such as methyl, ethyl, propyl, t-butyl,and the like, but also alkyl substituents bearing further substituentsknown in the art, such as hydroxy, alkoxy, alkylsulfonyl, halogen atoms,cyano, nitro, amino, carboxyl, etc. Thus, “alkyl group” includes ethergroups, haloalkyls, nitroalkyls, carboxyalkyls, hydroxyalkyls,sulfoalkyls, etc. On the other hand, the phrase “alkyl moiety” islimited to the inclusion of only pure open chain saturated hydrocarbonalkyl substituents, such as methyl, ethyl, propyl, t-butyl, and thelike.

The term “double bond” is non-limiting and refers to any type of doublebond between any suitable atoms (e.g., C, O, N, etc.). The term“ethylenically unsaturated” refers to compounds that include acarbon-carbon double bond (i.e. —C═C—).

As used herein, the term “glass transition temperature” or “Tg” refersto the temperature at which an amorphous, solid material undergoes areversible transition to a molten, rubber-like state. Unless otherwiseindicated, the Tg values described herein are theoretical valuespredicted using the Fox equation. Application of the Fox equation toestimate the Tg of polymers is well known in the art.

The term “component” refers to any compound that includes a particularfeature or structure. Examples of components include compounds,monomers, oligomers, polymers, and organic groups contained there.

Unless otherwise indicated, a reference to a “(meth)acrylate” compound(where “meth” is bracketed) is meant to include both acrylate andmethacrylate compounds.

The term “gloss” as used herein refers to the specular reflectance froma planar surface. Gloss is determined by projecting a beam of light offixed intensity and angle onto a surface and measuring the amount ofreflected light at an equal but opposite angle. As used herein, gloss ismeasured at angles of 20 and 60° using the procedure detailed in ASTMD523-14 (Standard Test Method for Specular Gloss).

The term “efflorescence” as used herein refers to various forms of colorchange and paint deterioration that occurs with painted masonry, stucco,concrete, stone work, and the like. In certain instances, crusty whitesalt deposits appear on painted masonry, concrete, stucco, or stonework. The deposits occur because mineral salts present in masonrymaterial, i.e. brick, concrete, and the like, dissolve in water overtime and then migrate to the surface of the masonry material and throughthe paint film as the water evaporates. The term “efflorescence” alsorefers to color shifts or color loss and deterioration that occurs onfresh (i.e. newly mixed or prepared) masonry, concrete, stucco, or stonework. For example, alkali burnout occurs because the pigments in awater-based paint may lack alkali resistance in the high pH environmentof fresh masonry, or the increase in pH of as moisture is introduced.

As used herein, the term “surfactant leaching” refers to a process wherea surface painted with a water-based latex paint develops stains orresidue on exposure to water over a period of time. This staining is theresult of surfactants and other hydrophilic or water-soluble formulationadditives in the paint that migrate to the surface of the paint film asthe water evaporates over time. The terms “exudation” and/or “weeping”may also be used interchangeably with “surfactant leaching.”

The term “tannin bleed-through” as used herein refers to a phenomenoncommon in painted wood surfaces, particularly exterior wood surfacessuch as siding, for example. Tannins and other extractables orextractive components in wood are soluble in water and tend to migrateor bleed through to the surface of the wood causing discoloration orstaining of the paint film applied on the wood surface. The term“extractive bleeding” may be used interchangeably with “tanninbleed-through.”

The term “on”, when used in the context of a coating applied on asurface or substrate, includes both coatings applied directly orindirectly to the surface or substrate. Thus, for example, a coatingapplied to a primer layer overlying a substrate constitutes a coatingapplied on the substrate.

Unless otherwise indicated, the term “polymer” includes bothhomopolymers and copolymers (i.e., polymers of two or more differentmonomers).

The term “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

As used herein, “a.” “an,” “the,” “at least one,” and “one or more” areused interchangeably. Thus, for example, a coating composition thatcomprises “an” additive can be interpreted to mean that the coatingcomposition includes “one or more” additives.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.). Furthermore, disclosure of a range includesdisclosure of all subranges included within the broader range (e.g., 1to 5 discloses to 4, 1.5 to 4.5, 1 to 2, etc.).

DETAILED DESCRIPTION

The present disclosure provides water-based compositions, such ascoating compositions, particularly paints, containing a latex or awater-dispersible polymer and a water-insoluble UV-VIS (preferably,ultraviolet) absorber. Preferably, the water-based compositions are inthe form of paints, although sealers, caulks, and sealants are withinthe scope of the present disclosure.

The water-based compositions of the present disclosure are advantageousin that they have a relatively low volatile organic (VOC) contentwithout sacrificing the balance of properties desired for an applied(i.e., dry) composition, such as a coating of paint. Governments haveestablished regulations setting forth guidelines relating to volatileorganic compounds (VOC) that may be released into the atmosphere. Suchregulations vary from region to region, but the most stringentregulations are in the South Coast region (e.g., Los Angeles County andOrange County, Calif.). Such regulations also vary by product. Forexample, clear topcoats can have no more than 200 grams per liter (g/l),water-borne coatings can have no more than 50 g/l, pigmented lacquerscan have no more than 275 g/l VOC.

Reducing the volatility of various paint additives such as, for example,coalescents, solvents, plasticizers, etc. can adversely affect thebalance of properties needed in water-based compositions, especiallywith respect to dirt pick-up. Thus, there is a need for compositionsthat possess desirable stability, compatibility, film formation ability,low dirt pick-up, etc.

Compositions of the present disclosure possess these properties whilepossessing low total VOC in the water-based compositions. In certainembodiments, the water-based compositions include no greater than 25grams per 100 grams polymer solids, or no greater than 20 grams per 100grams polymer solids, or no greater than 15 grams per 100 grams polymersolids, or no greater than 10 grams per 100 grams polymer solids, or nogreater than 5 grams per 100 grams polymer solids, or no greater than 2grams per 100 grams polymer solids.

Stated another way, in certain embodiments wherein the water-basedcompositions of the present disclosure are paints, they include nogreater than 25 grams per liter of paint, or no greater than 20 gramsper liter of paint, or no greater than 15 grams per liter of paint, orno greater than 10 grams per liter of paint.

In an embodiment, the present description provides methods andcompositions that include a non-VOC absorber. Suitable absorbers asdescribed herein include electromagnetic radiation absorbers such as,for example, ultraviolet absorbers, visible absorbers, and the like.These compounds are typically referred to as photoinitiators.

Suitable electromagnetic absorbers are water-insoluble electromagneticabsorbers. By this it is meant that the compounds will not dissolve toan appreciable extent in water at the temperatures typically used forpreparing water-based compositions as described herein.

In certain embodiments, suitable UV-VIS absorbers are those compoundscapable of absorbing ultraviolet and/or visible radiation within a rangeof 240-465 nm. For certain embodiments, they are capable of absorbingradiation in the 280-450 nm range. In certain embodiments, suitablevisible light absorbers are those compounds capable of absorbing visibleradiation within a range of 420 to 450 nm.

In certain embodiments, suitable ultraviolet (UV) absorbers are thosecompounds capable of absorbing UV radiation within a range of 240 to 400nm. For certain embodiments, they are capable of absorbing UV radiationin the 280 to 400 nm range, and for certain embodiments in the 315 to375 nm range.

The UV-VIS (preferably ultraviolet) absorbers do not form a bond to thepolymer, although they are capable of generating a radical through ahydrogen-abstracting mechanism by absorbing UV-VIS (typically UV)radiation. Without limiting to theory, it is believed that this resultsin surface crosslinking of the polymer.

Suitable examples of UV-VIS absorbers include, for example, thosedescribed in U.S. Pat. No. 9,120,936.

In an embodiment, the water-based compositions of the present disclosureinclude one or more UV-VIS (preferably UV) absorbers or photoinitiators.The UV absorber is preferably a non-VOC or zero-VOC compound that elutesafter the methyl palmitate marker in ASTM D6886. In a preferred aspect,the water-based compositions described herein preferably includes asingle non-VOC UV absorber that elutes after the methyl palmitatemarker, such as, for example, methyl-o-benzoyl benzoate (MBB) which hasthe structure shown below and is a commercially available under thetradename GENOCURE MBB (Rahn USA).

The amount of the UV-VIS (preferably, ultraviolet) absorbers present inthe water-based compositions of the present disclosure includes anamount that provides the desired result. In certain embodiments, thewater-based composition of the present disclosure includes a sufficientamount of the one or more water-insoluble UV-VIS (preferably,ultraviolet) absorbers to improve dirt pick-up resistance by at least10%, or at least 20%, or at least 30%, or at least 40%, or at least 50%,relative to the same water-based composition without the UV-VIS(preferably, ultraviolet) absorber, based on a change in ΔE values. TheUV-VIS (preferably, ultraviolet) absorber thus acts as a dirt-pick upresistant additive.

A coating discolors when it picks up dirt, or when efflorescence,surfactant leaching, tannin bleed-through and other such effects causestaining of the paint. ΔE is measured by a spectrophotometer bycomparing the paint that is exposed to dirt or otherwise stained, andthe paint that is “clean” of dirt. The difference is expressed as ΔE.The difference in ΔE's from the “control” paint and the “experimental”paint can then be calculated. The improvement in dirt pick-up resistanceor in resistance to efflorescence, surfactant leaching, extractivebleeding, and other effects can be expressed as a percentage by takingthe difference in ΔE divided by the ΔE of the “control” paint.

In certain embodiments, the water-based compositions of the presentdisclosure include at least 0.1 wt % of one or more UV-VIS (preferably,ultraviolet) absorbers, preferably greater than about 0.6%, morepreferably greater than about 0.9%, based on the weight of the polymersolids. In certain embodiments, the water-based compositions of thepresent disclosure include up to 5.0 wt %, preferably 0.6 to 4 wt %,more preferably 0.9 to 2 wt % of one or more UV-VIS (preferably,ultraviolet) absorbers, based on the weight of the polymer solids.

The water-based compositions described herein include a latex orwater-dispersible polymer. Such polymers are well known in the paint artand are typically particles emulsified or suspended in an aqueousmedium.

Suitable polymers are thermoplastic polymers with a relatively highmolecular weight (e.g., 50,000 to greater than 1,000,000 Daltons). Thepolymers can have a wide range of glass transition temperatures,depending on the desired properties of the resultant coating. Forexample, suitable polymers include those that have at least one Tgwithin a range of −20° C. to 70° C., more preferably −20° C. to 60° C.,most preferably −10° C. to 40° C.

Without limiting to theory, it is believed that polymers with high Tg(greater than about 20° C.) result in coating compositions or paintswith good dirt pickup resistance but poor resistance to tanninbleed-through and surfactant leaching. As a result, when used asexterior paints, these compositions do not demonstrate the desiredaesthetic or performance attributes.

Accordingly, in certain embodiments, and particularly when there is aneed to reduce or eliminate efflorescence, surfactant leaching, tanninbleed-through and similar effects, suitable polymers include those thathave at least one Tg within a range of less than 16° C., preferably lessthan about 13° C., more preferably less than about 10° C. In certainembodiments, suitable polymers include those that have at least one Tgwithin a range of about 5° C. to 20° C., more preferably about 8° C. to14° C.

Conventionally, when polymers with low Tg (less than 20° C.) are used inthe coating compositions described herein, the paints demonstrateoptimal resistance to tannin bleed-through and surfactant leachingeffects, but have poor dirt pickup resistance. Therefore, conventionalpaint compositions often do not have all the desired performanceattributes, especially when used as exterior paints, for example.

Surprisingly, and in contravention of bias and existing knowledge in theindustry, the compositions or paints described herein demonstrate anoptimal balance of properties. In certain embodiments, compositions orpaints as described herein have superior exterior durability (resistanceto efflorescence, tannin bleed-through, surfactant leaching and othersimilar effects) as well as superior dirt pickup resistance.

In an aspect, paints formulated from the coating compositions describedherein have superior performance characteristics, including superiordirt pickup resistance, extractive bleeding, and efflorescencecharacterized by ΔE values of less than about 8.0, preferably less thanabout 5.0, more preferably less than about 3.0. The paints also havesuperior resistance to surfactant leaching, characterized by less thanabout 0.3% extractables measured in the water phase, preferably lessthan 0.25%, more preferably less than about 0.2%.

In certain embodiments, when the polymer has at least one Tg less thanabout 10° C., a higher level of non-volatile UV absorber is preferred.Accordingly, in an aspect, water-based compositions of the presentdisclosure include at least 0.5 wt % of one or more UV-VIS (preferably,ultraviolet) absorbers, preferably greater than about 0.6%, morepreferably greater than about 0.9%, based on the weight of the polymersolids in the composition.

A variety of latex polymers may be employed in the disclosedcompositions including (meth)acrylics, vinyls, oil-modified polymers,polyesters, polyurethanes, polyamides, chlorinated polyolefins, andmixtures or copolymers thereof. Latex polymers are readily synthesizedat modest cost, and are typically prepared through chain-growthpolymerization, using one or more ethylenically unsaturated compounds(preferably monomers). Non-limiting examples of olefinic compounds whichmay be used to prepare latex polymers include ethylene, butadiene,propene, butene, isobutene, acrylic acid, methacrylic acid, methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexylacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate,butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl acrylate,hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutylacrylate, hydroxybutyl methacrylate, glycidyl methacrylate,4-hydroxybutyl acrylate glycidylether, acrylamide, methylacrylamide,styrene, α-methyl styrene, vinyl toluene, vinyl acetate, vinylpropionate, allyl methacrylate, acetoacetyl ethyl methacrylate (AAEM),diacetone acrylamide (DAAM), dimethylaminomethacrylate,diethylaminomethacrylate, N-hydroxy(meth)acrylamide, vinyl ethermaleate, vinyl esters of VERSATIC acid (VERSATIC acid is a syntheticsaturated monocarboxylic acid of highly branched structure containingabout 5 to about 10 carbon atoms), and mixtures thereof.

In certain embodiments, the latex polymer particles include ahomopolymer or copolymer including at least one of an acrylate or amethacrylate.

In certain embodiments, the water-based latex or water-dispersiblepolymer described herein is derived from the polymerization of one ormore emulsions containing ethylenically unsaturated monomers. Suitableethylenically unsaturated monomers include, for example, acrylic acid,alkyl and alkoxy acrylates or methacrylates (e.g., methyl methacrylate,butyl acrylate, 2-ethyl hexyl acrylate, butyl methacrylate, and thelike), vinyl esters of saturated carboxylic acids, monoolefns,conjugated dienes, optionally with one or more monomers, such as, forexample, styrene, vinyl acetate, acrylonitrile, acrylamide, diacetoneacrylamide, and vinyl chloride, and the like.

In a preferred aspect, the emulsions described herein may be preparedusing one or more monomers having readily abstractable hydrogen atoms.Suitable monomers of this type include, for example, 2-ethyl hexylacrylate (2-EHA), acetoacetoxy methacrylate (AAEM), and the like.Without limiting to theory, it is believed that these monomers enhancethe effectiveness of certain non-VOC UV absorbers, such as MBB forexample, as a dirt pickup-resistant additive.

The water-based latex or water-dispersible polymer described herein maybe a single stage latex or multistage latex (i.e. those with more thanone Tg). In such polymers, generally, there is a hard and a soft phaseso the Tg peaks could be −30° to 100° in the same polymer mixture.Frequently, these polymers are referred to as core-shell, but could alsobe other morphologies like “raspberry-like” or “acorn-like.” In anaspect, where the water-dispersible polymer described herein is amultistage latex, the average Tg of the polymer is within a range ofpreferably −20° C. to 70° C., more preferably −20° C. to 60° C., mostpreferably −10° C. to 40° C.

Suitable water-based or water-dispersible polymers also include“gradient” polymers in which there is a change in composition (or Tg)during polymerization. Often these types of polymers will not exhibit asharp inflection point corresponding to a single Tg value when measuredby DSC.

In certain embodiments, the water-based latex or water-dispersiblepolymer described herein is made by a single-stage process usingdiscrete, sequential charges of two or more monomers or monomermixtures, or was made using a continuously-varied charge of two or moremonomers.

In certain embodiments, the water-based latex or water-dispersiblepolymer described herein is made using a two-stage process. An exemplarytwo-stage process for making a water-based latex or water-dispersiblepolymer is described in U.S. Patent Application No. US 2014/0256868 A1.

Exemplary commercially available latex polymers include AIRFLEX EF811(available from Air Products), EPS 2533. EPS 2757, EPS 2792, EPS 2705(available from EPS/CCA) and NEOCAR 2300, NEOCAR 820 and NEOCAR 2535(now Arkema), RHOPLEX VSR 50, RHOPLEX VSR 2015, (available from DowChemical Co.), Optive 130 and OPTIVE 230 from BASF. Other exemplarylatex polymers include the latex polymers described in U.S. patentapplication No. US 2007/0110981 A1.

Surfactants suitable for use with latex polymers include, for example,sodium lauryl sulfate, sodium laureth sulfate (DISPONIL series fromBASF), sodium dodecyl benzene sulfonate, RHODAFAC RE 610, RHODAFAC RS410, RHODAFAC RS 610, RHODAFAC RS 710, ABEX EP 100, ABEX EP 110(Rhodia/Solvay), POLYSTEP B1, POLYSTEP B330 (Stepan, Northfield Ill.),sodium dioctyl sulfosuccinate, and the like.

Suitable water-dispersible polymers include polyurethanes, epoxies,polyamides, chlorinated polyolefins, acrylics, oil-modified polymers,polyesters, and mixtures or copolymers thereof, for example. Suchpolymers are readily synthesized and made to be water-dispersible usingconventional techniques. For example, the incorporation of amine or acidfunctionality produces water dispersibility.

Oil-modified polymers can also be used if desired. Such polymers arereadily synthesized and can be made to be water-dispersible usingconventional techniques. As used herein, oil-modified polymers arebroadly defined to include polymers that contain oils and/or oil-basedderivatives such as glyceride oils (monoglycerides, diglycerides, andthe like), fatty acids, fatty amines, and mixtures thereof. Examples ofsuch oil-modified polymers include, alkyds, oil-modified polyurethanes,oil-modified epoxies, oil-modified polyamides, oil-modified acrylics,and mixtures or copolymers thereof. Preferably, the oil-modified polymeris an oil-modified polyurethane or an alkyd.

The coating composition described herein is derived by polymerization ina single stage process of an emulsion including one or moreethylenically unsaturated monomers. In a preferred embodiment, thecoating composition described herein is made by a method that includesproviding one or more ethylenically unsaturated monomers in an emulsionthat is polymerized in a single-stage process. In an aspect, theemulsion includes about 20 to 60, preferably 30 to 55 percent by weightof methyl methacrylate; 0 to 40, preferably 10 to 30 percent by weightof 2-ethyl hexyl acrylate; 10 to 60, preferably 15 to 55 percent byweight of butyl acrylate; about 0 to 30, preferably 10 to 20 percent byweight of butyl methacrylate; and about 0 to 10, preferably 1 to 5percent by weight of methacrylic acid.

In certain embodiments, the coating composition described hereinoptionally includes a crosslinking component. Suitable crosslinkingcomponents are selected from one or more ethylenically unsaturatedmonomers including, for example, acrylic acid, methacrylic acid, methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexylacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate,butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl acrylate,hydroxyethyl methacrylate, hydroxybutyl acrylate, hydroxybutylmethacrylate, glycidyl methacrylate, 4-hydroxybutyl acrylate glycidylether, 2-(acetoacetoxy)ethyl methacrylate (AAEM), diacetone acrylamide(DAAM), acrylamide, methacrylamide, methylol (meth)acrylamide, styrene,α-methyl styrene, vinyl toluene, vinyl acetate, vinyl propionate, allylmethacrylate, and mixtures thereof. Preferred monomers for use as thecrosslinking component include AAEM, DAAM, and mixtures or combinationsthereof.

In certain embodiments, if a crosslinking component is used, the coatingcomposition described herein includes about 0 to 10, preferably 1 to 5percent by weight of the crosslinking component. In a preferred aspect,the crosslinking component includes AAEM, DAAM, and mixtures orcombinations thereof.

The amount of latex or water-dispersible polymers present in the coatingcompositions described herein includes an amount that provides thedesired result. Preferably, one or more polymers is used in an amount ofat least 10 wt %, based on 10 to 25% solids of the paint for flats and15 to 35% for semi-gloss paints. Preferably, one or more polymers arepresent in an amount of up to 25 wt %, based on solids.

Other components of the coating compositions descried herein includethose typically used in paint formulations, such as coalescents,pigments (in a pigment grind), fillers, thickeners, biocides,mildewcides, surfactants, dispersants, defoamers, and the like. Thecoating compositions can be made using standard techniques known in thepaint industry. Typical pigment volume concentrations (PVC) ranges forflat paints are 35 to 75 for semi-gloss are 20 to 40, while a high glosspaint has PVC ranges of about 10 to 25.

In an embodiment, the coating compositions described herein may be usedto make semi-gloss and high gloss paint formulations. By “semi-gloss” ismeant a paint finish that has a moderately satin-like luster and has a60° gloss rating of at least about 30, more preferably about 35 to 70units. A “high gloss” paint finish has a shiny appearance and reflectslight in a specular or mirror-like direction. High gloss paints have 60°gloss ratings of at least about 70, more preferably 70 to 85, and evenmore preferably, greater than 85 units.

Preferably, the coating compositions described herein include one ormore coalescent compounds having a relatively low volatile organiccontent (VOC), and more preferably, a low molecular weight. Typically,the volatile organic content of suitable coalescents, as determined byASTM D2369-90, is 30% or less, 20% or less, 15% or less, 11% or less, or10% or less, based on the original weight of the coalescent.

Examples of suitable low VOC coalescents for use in the coatingcompositions described herein include one or more compounds as describedin U.S. Pat. No. 8,440,752. Specific examples include, for example:tergitols (e.g., that are available under the trade name TERGITOL, suchas TERGITOL 15-S-15 from Dow), alkyl phthalate esters (e.g., dimethylphthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate,di-2-ethylhexyl phthalate, heptyl nonyl undecyl phthalate, butylcyclohexyl phthalate, and dicyclohexyl phthalate); aryl phthalate esters(e.g., diphenyl phthalate); alkyl aryl phthalate esters (e.g., butylbenzyl phthalate); alkyl citrate esters (e.g., tributyl citrate andtriethyl citrate); isosorbide di-alkyl ethers (e.g., dimethyl anddiethyl isosorbide ether); alkyl maleates (e.g., dioctyl maleate andbis(2-ethylhexyl) maleate); alkyl adipate esters (e.g., bis(2-ethyhexyl)adipate and dioctyl adipate); alkyl aryl adipate esters (e.g., benzyloctyl adipate); benzoate esters (e.g., diethylene glycol dibenzoate,isodecyl benzoate, oxtyl benzoate); azelates (e.g.,bis(2-ethylhexyl)azelate); ricinoleic acid esters; polyethylene glycolethers; tri(ethylene glycol)bis(2-ethylhexanoate); tetra(ethyleneglycol)bis(2-ethylhexanoate); glyceryl monooleate; octadecenoic acidmethyl ester, and oleic acid monoester of propylene glycol; and fattyacid/oil derivatives such as those available from ADM under the tradedesignation ARCHER PC.

Examples of preferred low VOC coalescents include bis(2-ethylhexyl)maleate, bis(2-ethylhexyl) adipate, bis(2-ethylhexyl) azelate, isodecylbenzoate, tri(ethylene glycol)bis(2-ethylhexanoate), tetra(ethyleneglycol)bis(2-ethylhexanoate), tributyl citrate, octyl benzoate,di(ethylene glycol)dibenzoate, octadecenoic acid methyl ester, and oleicacid monoester of propylene glycol.

These compounds can be formed using standard organic synthesistechniques, which are well known to one of skill in the art.

The amount of the one or more low VOC coalescents present in thewater-based compositions of the present disclosure includes an amountthat provides the desired result. Preferably, one or more relatively lowVOC coalescents, are present in a water-based composition in an amountof at least 1 wt-%, or at least 2 wt-%, or at least 3 wt-%, or at least4 wt-%, or at least 5 wt-%, based on polymer solids. Preferably, one ormore relatively low VOC coalescents are present in a water-basedcomposition in an amount of up to 10 wt-%, or up to 20 wt-%, based onpolymer solids. When mixtures of such coalescents are used, thenumerical values of the variables in the formulas described herein areaverages.

The types of additives that can be incorporated into a water-basedcomposition of the present disclosure depend on the use of thecomposition. For example, a paint includes one or more pigments(referred to as a pigment grind). A sealer may typically include adefoamer and possibly a surfactant. A caulk or sealant includes similaradditives to that of a paint.

In certain embodiments, a paint contains sufficient TiO₂ pigment to besubstantially visually opaque when applied at a thickness of 3 mil(0.0762 mm) and dried.

The UV-VIS (preferably, ultraviolet) absorber(s) can be incorporatedinto the compositions described herein using a variety of methods knownto those of skill in the art. An example of a suitable method includesmixing or dissolving the absorber into one or more low VOC coalescentsprior to adding the mixture or solution to a pigment grind component, ora polymer/pigment mixture. Another suitable example includes mixing ordissolving the absorber into one or more low VOC coalescents that aresubsequently added to a finished paint formulation.

In a preferred aspect, the UV-VIS (preferably, ultraviolet) absorberdescribed herein is added to a polymer emulsion mixture afterpolymerization is complete. For a single-stage system, a monomeremulsion including two or more monomers is fed to a reactor over aspecified period of time, and the UV-VIS absorber is added afterpolymerization is complete. For a two-stage system, a first monomer feedincluding two or more monomers is fed to a reactive over a specifiedperiod of time, following by a second monomer feed that includes two ormore monomers. The first and second monomer feeds may include the sameor different monomers, and these monomers may be present in the same ordifferent amounts in the first and second monomer feeds. The average Tgof the two stages is preferably between −10 and 40° C. The UV-VISabsorber is then added to the two-stage system after polymerization iscomplete.

Accordingly, in an embodiment, the coating composition described hereinis made by a method that includes: providing a water-dispersible polymerin an aqueous solvent; providing a non-VOC UV absorber capable ofabsorbing UV radiation within a range of 240 to 400 nm; and mixing thewater-dispersible polymer with the UV absorber in an amount sufficientto produce a coating composition with improved dirt pick-up resistancerelative to a conventional coating composition, based on ΔE values.

In an embodiment, the coating composition described herein is made by amethod that includes: providing one or more ethylenically unsaturatedmonomers in an emulsion; polymerizing the emulsion; and adding a non-VOCUV absorber capable of absorbing UV radiation in a range of about 240 to400 nm to the polymerized emulsion. In this method, the non-VOC UVabsorber is present in an amount sufficient to produce a coatingcomposition with improved dirt pick-up resistance relative to aconventional coating composition, based on ΔE values.

In another embodiment, the coating composition described herein is madeby a method that includes providing one or more ethylenicallyunsaturated monomers in a first monomer emulsion and a second monomeremulsion that are polymerized in a two-stage process. In an aspect, thefirst monomer emulsion includes about 10 to 30 percent by weight ofbutyl acrylate; 1 to 4 percent by weight acetoacetoxy ethylmethacrylate; 50 to 90 percent by weight of methyl methacrylate; and 1to 5 percent by weight of (meth)acrylic acid. The second monomeremulsion includes about 1 to 5 percent by weight of acrylic acid; 1 to10 percent by weight of diacetone acrylamide; 1 to 10 percent by weightof butyl acrylate; and 75 to 90 percent by weight methyl methacrylate.

EXAMPLES

The invention is illustrated by the following examples. It is to beunderstood that the particular examples, materials, amounts, andprocedures are to be interpreted broadly in accordance with the scopeand spirit of the inventions as set forth herein. Unless otherwiseindicated, all parts and percentages are by weight and all molecularweights are weight average molecular weight. Unless otherwise specified,all chemicals used are commercially available from, for example,Sigma-Aldrich, St. Louis, Mo.

Test Methods

Unless indicated otherwise, the following test methods were utilized inthe Examples that follow.

A. Dirt Pickup Resistance Test

Paint samples to be tested are applied to a 3×6 aluminum Q panel (orother appropriate substrate) using a wire wound drawdown bar (RDS) to afilm thickness of about 3 mils. Each paint sample is then dried for 24hours at room temperature (70-75° F.). Dried panels are placed outdoorsor in a QUVA cabinet for one week, with some exposure to sunlight.Outdoor testing is preferred, but QUVA exposure is acceptable.

The panels are then returned to the lab after one week exposure andblotted dry if necessary.

A “dirt” slurry is prepared as follows. First, 50 grams (g) red ironoxide (R4097), 40 g yellow oxide pigment, and 10 g black iron oxidepigment are combined and hand stirred or shaken until homogenous. Then0.5 g TAMOL 731 (Dow Chemical) is added to 200 g deionized water withagitation. The pigment combination is then slowly added and mixed for 30minutes until a smooth slurry is formed.

The slurry is applied to half of the coated panels using a foamapplicator or other suitable brush, and dried on panels at roomtemperature for 3-4 hours.

The dried slurry is then washed off each panel by running the panelunder water and using a small piece of cheese cloth, rubbing lightly. Aclean cloth is used for each panel. The panels are blotted dry andallowed to completely dry (2-4 hours) before measuring change in color,ΔE, using a spectrophotometer.

B. Measurement of Gloss

Specular gloss ratings for paint formulations applied to test panels aremeasured according to the procedure described in ASTM D523-14 (StandardMethod for Specular Gloss).

C. Measurement of Surfactant Leaching

To determine surfactant leaching, a paint is drawn down onto a blackmylar chart using a 6 mil drawdown bar. The drawdown is dried for 4hours at room temperature. 5 g of water is pipetted onto the drawdown,keeping care to apply the water in as small of a surface area as thecoating allows. The water is allowed to sit for 30 minutes, after which,the water is collected and analyzed for extractables using LiquidChromatography-Mass Spectroscopy (LC-MS).

D. Measurement of Efflorescence

In order to perform efflorescence testing, the white paint was tinted ina half-pint sized-can with two colorants. 248.6 grams of white paint wastinted with 24 grams of Novocolor 8544C Quinacridone Red, and 14 gramsof Novocolor 8513 Yellow colorant. The tinted paints were then shakenfor approximately 5 minutes. Before painting, each tinted paint wasdrawn down on a plain white penopac chart, using a 3 mil draw down bar,and stored in a drawer to preserve the color. The substrates used forefflorescence testing were Hardie Boards skim-coated with UGL Drylok.Once dried, the board was split off into 6 equal length sections. Thesesections were painted with 400 square feet per gallon amount of paint,which equated to 6 grams. After completing the first coats of eachsection, the board was left to dry approximately 2 hours beforefinishing with a second coat on each section. They were then allowed todry at room temperature overnight and then put outside for exteriorexposure the following day. The panels were exposed outside for 24 days.The panels were then brought inside and measured on a spectrophotometer,measuring a ΔE value of the current color after being exposed, comparedto its initial color, on the draw down chart taken initially.

E. Measurement of Tannin Stain Blocking

To evaluate the tannin stain blocking, a redwood board is painted withtwo coats (4 hours in between coats) of white paint. The board isallowed to dry for 1 to 2 days, after which the board is placed into ahumidity cabinet for 3 days. After removal from the cabinet, the boardis allowed to dry overnight and ΔE values are measured to evaluate colorchange.

Example 1. Preparation of Paint Compositions

Single stage latex polymer compositions were prepared by combiningmonomers including methacrylic acid (MAA), methyl methacrylate (MMA),n-butyl methacrylate (BMA) and/or 2-ethyl hexyl acrylate (EHA) in theamounts shown in Table 1. Emulsions #1 and #2 in Table 1 were preparedaccording to standard methods known to those of skill in the art. Theemulsions were fed into a reactor over a three-hour time period. Afterpolymerization was complete, a non-VOC UV absorber or photoinitiator wasadded to each emulsion. A white paint formulation and a clear paintformulation were prepared from the emulsions and tested for dirt pick upresistance, efflorescence, tannin bleed-through (white) and surfactantleaching (clear). The Tg values for each emulsion were measured bydifferential scanning calorimetry (DSC).

TABLE 1 Polymer Compositions Measured MAA MMA BA EHA Midoint Tg Emulsion(%) (%) (%) (%) (° C.) 1 1.5 44 40.3 10 14.2 2 1.5 44 30.7 20 11.7

Example 2. Performance Testing

Test paint formulations A and B were made from emulsions #1 and #2 fromExample 1 and applied to 3×6 aluminum Q panels. The dirt pick upresistance, efflorescence and tannin bleed-through of each formulationwas evaluated according to procedures described above. Four test panelswere prepared and results were averaged. Surfactant leaching wasassessed by measuring the amount of extractables in the water phase,specifically polyethylene glycol (PEG 400) using LC-MS. For comparison,paint formulations C and D were prepared using two commerciallyavailable all-acrylic latex polymers, Acronal OPTIVE 230 (BASF) andRHOPLEX 585 (Dow) and evaluated for the same performancecharacteristics.

Results are reported in Table 2. Surfactant leaching is reported as apercent of extractables and dirt pickup resistance is reported as achange in color or ΔE reading from a spectrophotometer.

TABLE 2 Performance Testing Dirt Pick Up Resistance PEG EfflorescenceTannin Paint (ΔE) (%) (ΔE) (ΔE) A 3.67 0.22 2.57 3.67 B 4.62 0.20 2.073.75 C 15.89 0.36 4.19 9.96 D 8.72 0.36 3.32 —

Example 3. Preparation of a Two-Stage Polymer Composition

A two-stage latex polymer was prepared by making a first monomeremulsion including 11.5 g acrylic acid, 6.5 g methacrylic acid, 30 gdiacetone acrylamide, 400 g butyl methacrylate, and 120 g methylmethacrylate. This first monomer emulsion was fed into a reactor over atwo-hour time period. A second monomer emulsion including 7.6 g acrylicacid, 14 g butyl acrylate, 13 g diacetone acrylamide, and 210 g methylmethacrylate was then fed into the reactor over a one-hour time period.After polymerization was complete, a non-VOC UV absorber orphotoinitiator was added to the emulsion. A paint formulation wasprepared from the emulsion.

The complete disclosure of all patents, patent applications, andpublications, and electronically available material cited herein areincorporated by reference. The foregoing detailed description andexamples have been given for clarity of understanding only. Nounnecessary limitations are to be understood therefrom. The invention isnot limited to the exact details shown and described, for variationsobvious to one skilled in the art will be included within the inventiondefined by the claims. The invention illustratively disclosed hereinsuitably may be practiced, in some embodiments, in the absence of anyelement which is not specifically disclosed herein.

What is claimed is:
 1. A water-based coating composition, comprising: alatex polymer having at least one Tg within a range of −10° C. to 40°C., wherein the latex polymer is derived by polymerization in a singlestage emulsion process, the emulsion comprising: 20 to 60 wt-% methylmethacrylate; 0 to 40 wt-% 2-ethyl hexyl acrylate; 10 to 60 wt-% butylacrylate; 0 to 30 wt-% butyl methacrylate; and 0 to 10 wt.-% methacrylicacid; a non-volatile UV absorber capable of absorbing UV radiationwithin a range of 240 to 400 nm; and a crosslinking component selectedfrom 2-(acetoxyacetoxy)ethyl methacrylate (AAEM), diacetone acrylamide(DAAM), and mixtures or combinations thereof; wherein the coatingcomposition includes no greater than 5 grams total VOC per 100 gramspolymer solids.
 2. The composition of claim 1 wherein the UV absorbercomprises methyl-o-benzoyl benzoate.
 3. The composition of claim 1wherein the UV absorber is present in an amount of at least 0.1 wt-% andup to 5.0 wt-%, based on the weight of the polymer solids.
 4. Thecomposition of claim 1 wherein the latex polymer is present in thecoating composition in an amount of at least 10 wt-%, based on 10-25%solids of the composition for flat paints and 15-35% for semi-glosspaints.
 5. The composition of claim 1 wherein the latex polymer isderived by polymerization in a single stage emulsion process, theemulsion comprising 10 to 30 wt-% 2-ethyl hexyl acrylate.
 6. Thecomposition of claim 1 wherein the latex polymer is derived bypolymerization in a single stage emulsion process, the emulsioncomprising 10 to 20 wt-% butyl methacrylate.
 7. The composition of claim1 comprising 1 to 5 wt-% of the crosslinking component.
 8. Thecomposition of claim 1 wherein the composition is a water-based paint,sealer, caulk, or sealant.
 9. The composition of claim 8 wherein thecomposition is a water-based paint.
 10. The composition of claim 9wherein the composition is a water-based paint with a pigment volumeconcentration of 35 to 75 for a flat paint, 20 to 40 for a semi-glosspaint, and 10 to 25 for a high gloss paint.
 11. The composition of claim9 wherein the composition is a semi-gloss paint having a paint finishthat has a 60° gloss rating of at least 30 units.
 12. The composition ofclaim 9 wherein the composition is a high-gloss paint having a paintfinish that has a 60° gloss rating of at least 70 units.
 13. Thecomposition of claim 1 wherein the composition has extractables of lessthan 0.3%.
 14. The composition of claim 1 wherein the latex polymer hasat least one Tg within a range of 5° C. to 20° C.
 15. The composition ofclaim 1 wherein the composition includes no greater than 2 grams totalVOC per 100 grams polymer solids.
 16. The composition of claim 14further comprising one or more low VOC coalescents having a volatileorganic content of 30% or less.
 17. A water-based coating composition,comprising: a latex polymer having at least one Tg within a range of 5°C. to 20° C., wherein the latex polymer is derived by polymerization ina single stage emulsion process, the emulsion comprising: 20 to 60 wt-%methyl methacrylate; 0 to 40 wt-% 2-ethyl hexyl acrylate; 10 to 60 wt-%butyl acrylate; 0 to 30 wt-% butyl methacrylate; and 0 to 10 wt-%methacrylic acid; 0.1 to 5.0 wt-% methyl-o-benzoyl benzoate, wherein theweight percent is based on the weight of the polymer solids; and acrosslinking component selected from 2-(acetoxyacetoxy)ethylmethacrylate (AAEM), diacetone acrylamide (DAAM), and mixtures orcombinations thereof; wherein the coating composition includes nogreater than 5 grams total VOC per 100 grams polymer solids.
 18. Thecomposition of claim 17 wherein methyl-o-benzoyl benzoate is present inan amount of 0.6 wt-% to 5.0 wt-%, based on the weight of the polymersolids.
 19. The composition of claim 17 wherein the latex polymer ispresent in the coating composition in an amount of at least 10 wt-%,based on 10-25% solids of the composition for flat paints and 15-35% forsemi-gloss paints.
 20. The composition of claim 17 wherein the latexpolymer is formed from reactants comprising acrylamide in an amount ofno more than 10 wt-%.
 21. The composition of claim 17 wherein a coatingformed from the coating composition has a dirt pick-up resistancerepresented by ΔE values of less than 8.0 units.